1. Field of the Invention
The present invention relates to a gallium nitride group compound semiconductor light-emitting device, which is capable of emitting light from the visible region to the ultraviolet region of the light spectrum, and more specifically, the present invention relates to a gallium nitride group compound semiconductor light-emitting device having a semiconductor layer which it formed on a substrate and includes a light-emitting region.
2. Description of the Related Arts
FIG. 10 Illustrates a conventional gallium nitride group compound semiconductor light-emitting device 600.
The gallium nitride group compound semiconductor light-emitting device 600 includes: a insulative sapphire substrate 61; an N-type gallium nitride group compound semiconductor layer 62 and a P-type gallium nitride group compound semiconductor layer 63 formed on the substrate in this order and a light-transmittable thin film electrode 64 for the P-type gallium nitride group compound semiconductor layer 63, an insulation layer 65, and a fluorescent material layer 66 formed thereon in this order.
Light emitted from the semiconductor layers 62 and 63 is transmitted through the light-transmittable thin film electrode 64 and the insulation layer 65, and then enters the fluorescent material layer 66, where the light is converted into visible light having a different wavelength and then is emitted to the outside of the device.
However, the conventional gallium nitride group compound semiconductor light-emitting device 600 has the following problems.
The gallium nitride group compound semiconductor light-emitting device 600 is characterized by having the light-transmittable thin film electrode 64 formed on the surface of the P-type gallium nitride group compound semiconductor layer 63, and the insulation layer 65 and the fluorescent material layer 66 formed thereon in this order.
Therefore, in order to increase the light-emitting power of the respective N-type and P-type gallium nitride group compound semiconductor layers 62 and 63, which are positioned under the fluorescent material layer 66, the light-transmittable thin film electrode 64 is required to maintain a light-transmitting characteristic from the visible region to the ultraviolet region of the light spectrum. Therefore, the light-transmittable thin film electrode 64 has to be practically formed as a thin film having a film thickness of about 10 nm.
In addition, in the case where the wavelength of the light is transformed by the fluorescent material layer 66, the fluorescent material layer 66 has to be formed as a layer having a thickness of 2 xcexcm or more. This causes a problem in that the light-transmittable thin film electrode 64 cracks due to the heat strain created during the formation of the fluorescent material layer 66.
If the light-transmittable thin film electrode 64 cracks, the current flowing in the light-transmittable thin film electrode 64 becomes irregular, thereby making the emission of the gallium nitride group compound semiconductor light-emitting device 600 irregular.
Furthermore, the cracks increase the resistance of the light-transmittable thin film electrode 64. As a result, the driving voltage of the device increases and the reliability of the device is reduced.
According to one aspect of the invention, there is provided a semiconductor light-emitting device including: a substrate; a semiconductor layer including at least a light-emitting region; a metal layer having a light transmitting characteristic; a first fluorescent material layer for transforming at least a portion of first light emitted from the light-emitting region into second light having a different wavelength from the first light; and an oxide semiconductor layer formed between the metal layer and the first fluorescent material layer and having alight transmitting characteristic.
In one embodiment of the invention, the semiconductor layer is formed of a gallium nitride group compound semiconductor.
In another embodiment of the invention, the metal layer to formed of an ohmic metal thin film.
According to the structure described above, the oxide semiconductor layer which has a light transmitting characteristic is provided between the metal thin film (which has a light transmitting characteristic and is formed on the semiconductor layer) and the first fluorescent material layer. Therefore, even if a crack is created on the metal thin film, the current flows evenly in the metal thin film via the oxide semiconductor layer, thereby enabling a uniform emission from the light-emitting region and improving the reliability of the device.
Furthermore, the oxide semiconductor layer has a good adhesion, a good mechanical strength, a low moisture transmission, and a good thermal stability. Therefore, when the fluorescent material layer is formed, the oxide semiconductor layer is capable of acting as a protection layer for the metal thin film.
In addition, by forming the oxide semiconductor layer which acts as a layer for protecting the metal thin film and improving the conductivity, and providing the fluorescent material layer thereon, a gallium nitride group compound semiconductor light-emitting device is provided which is suitable for mass-production and effectively emits light to the outside of the device.
In still another embodiment of the invention, a thickness of the metal layer is from about 1 nm to about 10 nm.
According to the structure described above, the metal thin film formed on the semiconductor layer is designed to have a suitable thickness, thereby making it possible to provide a metal thin film having good transmittance without reducing an ohmic characteristic between the semiconductor layer and the metal thin film. As a result, a uniform light-emitting pattern is obtained in the light-emitting region of the semiconductor layer.
In still another embodiment of the invention, a thickness of the oxide semiconductor layer is from about 0.1 xcexcm to about 1 xcexcm.
In still another embodiment of the invention, the oxide semiconductor layer includes at least one of the materials selected from the group consisting of In2O3, SnO2, ZnO, Cd2SnO4, and CdSnO3.
According to the structure described above, the oxide semiconductor layer having a light transmitting characteristic formed on the metal thin film is designed to have a suitable thickness, thereby mating it possible to provide an oxide semiconductor layer which is excellent in conductivity and durability, and transmits a large portion of light emitted from the light-emitting region. As a result, a highly efficient and highly reliable device is provided, in which a uniform light-emitting pattern is obtained in the light-emitting region of the semiconductor layer.
In still another embodiment of the invention, a first electrode is formed on a portion of the metal layer.
According to the structure described above, the first electrode is formed directly on the metal thin film. Therefore, it is possible to inject the current effectively and directly into the device.
In still another embodiment of the invention, a second electrode is formed on a portion of the oxide semiconductor layer.
According to the structure described above, the oxide semiconductor layer is formed on the entire surface of the metal thin film, thereby a better ohmic characteristic between the semiconductor layer and the metal thin film is achieved. As a result, it is possible to inject the current evenly from the second electrode.
In still another embodiment of the invention, a conductive wire is formed on a portion of the oxide semiconductor layer.
According to the structure described above, external connection means, such as an Au wire is directly provided on the oxide semiconductor layer, so as to eliminate the second electrode. Therefore, the manufacturing process of the device is simplified, thereby reducing the manufacturing time and the device cost.
In still another embodiment of the invention, a bottom surface area of the metal layer is smaller than a bottom surface area of the oxide semiconductor layer; and a second fluorescent material layer is formed on each side face of the oxide semiconductor layer and the semiconductor layer.
In still another embodiment of the invention, a third fluorescent material layer is formed on a side face of the substrate.
According to the structure described above, effects of the fluorescent material layers formed on the side faces of the semiconductor layers or the substrate do not influence the metal thin film. Therefore, a better ohmic characteristic between the metal thin film and the semiconductor layer is achieved. In addition, the fluorescent material layers effectively convert the wavelength of the light emitted in a side direction from the light-emitting region into a desired wavelength. Therefore, a device suitable for mass-production is provided.
In still another embodiment of the invention, the first fluorescent material layer is obtained by laminating a plurality of fluorescent material layers, each of the plurality of fluorescent material layers having different light-emitting wavelengths from one another.
In another aspect of the invention, a semiconductor light-emitting device includes: a substrate; at least one first conductive semiconductor layer; a plurality of second conductive semiconductor layers provided on the at least one first conductive semiconductor layer with a predetermined width between each other; a plurality of metal layers having a light-transmitting characteristic; and a plurality of metal oxide layers having a light-transmitting characteristic, wherein: the at least one first conductive semiconductor layer and the plurality of second conductive semiconductor layers provide a plurality of light-emitting regions; the semiconductor light-emitting device further includes: the plurality of fluorescent material layers for converting at least a portion of first light emitted from at least one of the light-emitting region into second light having a different wavelength from the first light; and a plurality of oxide semiconductor layers formed between the plurality of metal layers and the plurality of fluorescent material layers, and having a light-transmitting characteristic; and each of the plurality of fluorescent material layers has a light-emitting wavelength different from each other.
In one embodiment of the invention, the at least one first conductive semiconductor layer and the plurality of second conductive semiconductor layers are each formed of a gallium nitride group compound semiconductor.
According to the structure described above, it is possible to simultaneously produce devices which emit light of different wavelengths to one another; without reducing the ohmic characteristics between the semiconductor layer and the metal thin film. Therefore, comparing to the prior art, the present invention makes it easier to provide a light-emitting device capable of emitting light having a plurality of wavelengths (for example, the three primary colors of light, i.e., red, green and blue), with substantially the same size as the conventional device. In addition, it is possible to produce devices which emit light of different wavelengths to each other at the same time. Therefore, normalization of the device characteristics in facilitated.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.